Embodiments of the present invention relate to a rotatable-drum laundry drier, and to a method of controlling a rotatable-drum laundry drier.
The present invention relates to a rotatable-drum laundry drier, and to a method of controlling a rotatable-drum laundry drier.
Methods of controlling rotatable-drum laundry driers are known, in which: hot air is fed into the rotating drum so as to flow over the laundry inside; the impedance of the laundry is measured by measuring electrodes positioned contacting the laundry; the moisture of the laundry is determined on the basis of the impedance measurement; and the drying cycle is stopped when the impedance measurement reaches a substantially time-constant comparison threshold associated with a predetermined final moisture.
Tests conducted by the Applicant show that the actual moisture of the laundry at the end of the drying cycle using the above methods differs from the predetermined final moisture, depending on the quantity/weight of the laundry in the drum, and the difference is particularly marked when drying certain types of laundry, such as cotton, and/or synthetic fabrics.
FIG. 1 shows an example graph of the moisture of different quantities/weights of cotton laundry, as determined by the Applicant on the basis of laboratory drying test measurement data on a prior art laundry drier. As can be seen, using the control methods described above (in which the impedance of the laundry is compared with a time-constant comparison threshold), loads ranging between roughly 1 kg and 8 kg show a laundry moisture percentage ranging between roughly 24% and 11% of the laundry weight respectively. In other words, a 7 kg difference in load produces a 13% difference in final moisture, which is obviously unacceptable.
To achieve a precise, stable final moisture, regardless of the quantity/weight of the laundry, an electronic control system has been proposed, configured to determine the quantity/weight of the laundry in the drum using weight sensors, and to adjust the comparison threshold accordingly. This solution, however, is expensive and complicated to produce.
The Applicant has therefore researched thoroughly into devising a straightforward, low-cost solution designed to achieve a precise, stable final moisture, regardless of the quantity/weight of the laundry in the drum.
It is therefore an object of the present invention to provide a solution designed to achieve the above goals.